Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize solid state lighting (“SSL”) devices (e.g., LEDs) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIG. 1A is a cross-sectional view of a conventional SSL device 10a with lateral contacts. As shown in FIG. 1A, the SSL device 10a includes a substrate 20 carrying an LED structure 11 having an active region 14, e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”), positioned between N-type GaN 15, and P-type GaN 16. The SSL device 10a also includes a first contact 17 on the P-type GaN 16 and a second contact 19 on the N-type GaN 15. The first contact 17 typically includes a transparent and conductive material (e.g., indium tin oxide (“ITO”)) to allow light to escape from the LED structure 11. FIG. 1B is a cross-sectional view of another conventional LED device 10b in which the first and second contacts 17 and 19 are opposite of each other, e.g., in a vertical rather than lateral configuration. During formation of the LED device 10b, a substrate 20, similar to the substrate 20 shown in FIG. 1A, initially carries an N-type GaN 15, an active region 14 and a P-type GaN 16. The first contact 17 is disposed on the P-type GaN 16, and a carrier 21 is attached to the first contact 17. The substrate 20 is removed, allowing the second contact 19 to be disposed on the N-type GaN 15. The structure is then inverted to produce the orientation shown in FIG. 1B. In the LED device 10b, the first contact 17 typically includes a reflective and conductive material (e.g., aluminum) to direct light toward the N-type GaN 15.
As discussed in more detail below, the various elements of the SSL devices typically have different coefficients of thermal expansion (CTE). During temperature excursions that occur in manufacturing processes and/or during use, the difference in CTEs of the device elements may cause the elements to crack or delaminate. Due to differences in the coefficient of thermal expansion (CTE) for the various elements that form the wafers used for SSL manufacturing, and in particular, the CTE of sapphire relative to the CTE of GaN, wafers over four inches in diameter may be difficult to produce in a manner that results in high yields. Accordingly, there remains a need for substrates that improve the performance and reliability of the resulting device, and that reduce the cost and time associated with manufacturing such devices.